Everybody is ignoring the one thing that ACTUALLY makes the keys unique and could very well substantiate the "feeling" of each key: ratios. In equal temperament, none of the keys has the same ratios of resonance between scale degrees, since Pythagorean ratios had to be discarded to make every key palatable. So every key, regardless of A440 or another base, has its own microtonalities, which could very well explain the differing senses of tension in each key.

Everybody is ignoring the one thing that ACTUALLY makes the keys unique and could very well substantiate the "feeling" of each key: ratios. In equal temperament, none of the keys has the same ratios of resonance between scale degrees, since Pythagorean ratios had to be discarded to make every key palatable. So every key, regardless of A440 or another base, has its own microtonalities, which could very well explain the differing senses of tension in each key.

Actually, "this sort of thing" is – to me – one of the most interesting aspects of the “historical 'musical arts.'”

Throughout musical history, “pragmatic practitioners of the musical arts,” dependent though they might have been upon the patronage of this-or-that white-wigged scion of hereditary nobility, were always interested in the mathematics behind music ... whether they lived in the age of “equal temperament” or not.